Hazard for insulation and relevant EMC problems due to voltages in circuits of motor supply by PWM converters

The voltage hazard for insulation of power converter circuits is analysed. Selected EMC problems and especially the problem of higher harmonics of the current in a drive AC system, supplied from transistorised PWM converter, are discussed. Due to great steepness of voltage rise and decrease, resulting from PWM at the converter output, considerable capacitive currents appear, which are influencing the insulation durability and make the problem of protection against electrical shock difficult. The problem of higher harmonics of the current flowing from mains to the 7.5 kW converter has been considered. The efficiency of harmonics limitation by network reactors has been measured. Experimental results have been presented and relevant conclusions have been formulated.